1. Field of the Invention
This invention relates to a plastic food tray, and more particularly, a tray with a lid or cover which is lockable to the tray.
2. Description of the Prior Art
Food has been sold by "fast-food" restaurants in carry-out containers consisting of a thermoformed plastic tray provided with a hinged lid. The lid includes a flange which has been heretofore seated in snap arrangement with a horizontal flange integrally molded about the rim portion of the food-carrying tray. Attempts to hold the lid in a closed position on the flange about the rim portion of the tray while maintaining the ability to repeatedly open and close the tray without any degradation to the locking mechanism, have generally proved unsuccessful.
Such attempts have taken the form of providing an upstanding or vertical wall about the perimeter or periphery of the horizontal flange on the rim portion of the tray wherein the distance between opposed portions of the upstanding wall has been slightly less than the distance between corresponding portions of the mating flange on the lid so that the flange on the lid is engaged between opposed portions of the vertical wall on the perimeter of the horizontal tray flange in tight, interference fit. Because of the resiliency inherent in the hinge attaching the lid to the tray, this technique has enjoyed limited success. Further, because of the materials, such as plastic, used to form the tray, the distances between opposite portions of the upstanding wall and corresponding portions of the horizontal flange on the lid have been imprecise, therefore failing to effect a tight fit of the lid between opposite portions of the upstanding wall.
In order to remedy this, interlocking upright cylindrical elements have been formed on the horizontal flanges of the lid and tray. However, imprecision in the formation of the interlocking cylindrical elements and the inherent resiliency in the hinge of the lid prevented this from being a satisfactory mass-produced locking mechanism.
U.S. Pat. No. 4,576,330, issued to Schepp and having a common assignee as the instant invention, discloses a folding plastic food tray with interlocking male and female elements formed, respectively, on the horizontal flanges of the tray and lid. A snap, reversible locking engagement is realized by providing the male element with an enlarged diameter portion at its closed top end which is received in snap engagement past a smaller diameter annular rim formed in the opening to the bore of the female element. This configuration, however, has proven somewhat unsatisfactory in that in order to engage the male and female elements in snap, reversible locking engagement, one must press directly upon the male and female elements. In both this particular design and any other design using interlocking male and female elements, this pressure on the cylindrical elements may cause these elements, most notably the female element, to deform, thereby degrading the reliability of the locking arrangement. This deformation of the elements may result from repeated closing and opening of the tray, or may be due to minor misalignment of the elements immediately prior to engagement.
It is therefore an object of the present invention to provide a means whereby various designs of interlocking male and female elements, not limited to the above-described design of the Schepp patent, for interlocking the lid to a food tray are less susceptible to deformation in the engaging of this interlocking arrangement. This allows the repeated engagement and disengagement of the interlocking arrangement without any degradation thereto, and facilitates engagement of the interlocking elements despite minor misalignments during the engagement process. Such minor misalignments are inevitable with a folding lid design.